Inheritance of apple proliferation resistance by parental lines of apomictic <Emphasis Type="Italic">Malus sieboldii</Emphasis> as donor of resistance in rootstock breeding

To study inheritance of Malus sieboldii-derived apple proliferation resistance, 14 cross combinations were performed with the tetraploid apomictic M. sieboldii and first and second generation parental lines as donor of resistance and Malus x domestica scion cultivars and apple rootstocks as donor of pomological traits. In the progeny examined mainly three classes were present consisting of mother-like plants with the allele composition of the maternal apomict (ML), hybrids based on fertilization of an unreduced egg cell (hybrid I), and fully recombinant plants (hybrid II). Two-year screening of inoculated plants in the nursery revealed that progeny classes ML and H I responded similarly to infection and that about half of the progeny showed satisfactory resistance. No appropriate resistance was identified in progeny class H II. This might be due to the fact that in fully recombinant offspring M. sieboldii haplotypes have been reduced from 4n to 1-2n or were entirely lost. Following nursery-growing, promising trees were evaluated for six more years in the orchard. Nearly all of them showed satisfactory resistance but were mostly less productive and more vigorous than trees on clonal standard rootstock M9. However, mainly among the offspring of progeny 4608 × M9, resistant genotypes were identified showing pomological properties similar to M9.     

Apple proliferation resistance of <Emphasis Type="Italic">Malus sieboldii</Emphasis>-based rootstocks in comparison to rootstocks derived from other <Emphasis Type="Italic">Malus</Emphasis> species

In three trials carried out over a period of 24 years, open-pollinated seedlings of Malus sieboldii and M. sargentii and 22 apomictic rootstock selections with either M. sieboldii, M. sargentii or M. hupehensis in their parentage were examined for apple proliferation (AP) resistance in comparison to clonal M. x domestica-based rootstocks M 9, M 11, M 13, stocks of the B (Budagovski) and the Polish P series and M. robusta seedlings. Following experimental inoculation or natural infection the Golden Delicious-grafted trees on most of the M. sieboldii-derived progenies showed a high level of AP resistance expressed by low cumulative disease indices, a high percentage of non or little affected trees, low incidence of the small fruit symptom and non or little effect on vigour. Trees on M 9 and M 11, B 118 and M. robusta seedlings were moderately susceptible while trees on progenies with M. sargentii and M. hupehensis parentage, rootstocks of the P series, B 9, B 490 and M 13 proved highly susceptible. The screening also showed that rootstocks with M. sieboldii and M. sargentii parentage are often highly susceptible to latent apple viruses. Trees on most of the M. sieboldii-based progenies were more vigorous than trees on standard stock M 9, whereas the vigour of some progenies from selections with M. sargentii parentage was in the range of M 9 or even lower. Productivity was often correlated with the vigour.     

In vitro screening for resistance to apple proliferation in Malus species

A screening system for apple proliferation resistance was developed, based on in vitro graft‐inoculation with the causal agent ‘Candidatus Phytoplasma mali’. For this, in vitro cultures of the field‐resistant apomictic genotypes Malus sieboldii, H0909, D2212 and the susceptible Malus × domestica genotypes Golden Delicious and rootstock M9 were established, as well as in vitro cultures of Rubinette and Golden Delicious infected with ‘Ca. P. mali’ strains PM4 and PM6, respectively. Healthy in vitro shoots were inoculated by micrografting with infected shoots used as graft tip. After 6 weeks graft contact no significant differences for graft quality were observed between healthy and infected grafts. Mortality of grafts and transmission rates were not significantly different among the different genotypes. The phytoplasma concentration in inoculated shoots was determined at different times post‐inoculation (p.i.) by quantitative real‐time PCR. Infected M. sieboldii and D2212 had lower phytoplasma concentration than the susceptible controls and showed no symptoms. H0909 showed an intermediate behaviour exhibiting lower phytoplasma concentrations with strain PM4 but growth was affected. The dynamics of phytoplasma concentration reached a maximum at 6–8 months p.i. for all genotypes but the values for 3–5 and 10–12 months p.i. were similar. The resistance of M. sieboldii and D2212 was confirmed in vitro. A significant difference in phytoplasma concentration was observed between strains PM4 and PM6.     

Range of phytoplasma concentrations in various plant hosts as determined by competitive polymerase chain reaction

ABSTRACT For competitive polymerase chain reaction (PCR), an internal standard DNA template was developed that consisted of a highly conserved, internally deleted 16S rDNA fragment of an aster yellows phytoplasma. The internal standard was calibrated using a quantified culture of Acholeplasma laidlawii. Serial dilutions of the internal standard and fixed amounts of target templates from infected plants were coamplified with the same primers, and the products obtained were quantified using an enzyme-linked immunosorbent assay procedure. Analysis of the data revealed that the phytoplasma concentration in the plants examined differed by a factor of about 4 x 10(6). Phytoplasma concentrations of 2.2 x 10(8) to 1.5 x 10(9) cells per g of tissue were identified in periwinkles infected with various phytoplasmas. High to moderate concentrations were detected in Malus domestica (apple) genotypes infected with the apple proliferation phytoplasma, Alnus glutinosa (alder) genotypes infected with the alder yellows phytoplasma, and most aster yellows-infected Populus (poplar) genotypes examined. Very low phytoplasma concentrations, ranging from 370 to 34,000 cells per g of tissue, were identified in proliferation-diseased apple trees on resistant rootstocks 4551 and 4608, yellows-diseased Quercus robur (oak) trees, and Carpinus betulus (hornbeam) trees. Such low concentrations, which corresponded to about 4 to 340 cells in the reaction mixture, could only be detected and quantified by nested PCR.     

Pear decline resistance in progenies of <Emphasis Type="Italic">Pyrus</Emphasis> taxa used as rootstocks

Progenies of 39 open-pollinated genotypes belonging to 26 Pyrus taxa were examined for pear decline resistance and pomological traits when used as rootstocks. Following graft inoculation and observation over 18 years, considerable differences in pear decline resistance between and within the progenies were observed. Not affected or little affected and moderately to severely affected trees were observed in all progenies. However, great quantitative differences among them were observed. In the progenies of about one third of the pollinated trees most of the individuals showed a high level of resistance to grafted trees. Significantly different from this group was another third of the progenies that mostly showed high susceptibility in grafted trees. Between these two groups there were progenies that statistically neither differed from the resistant nor from the susceptible group. These progenies were defined as moderately resistant. Significant differences in resistance were also observed between progenies of genotypes of the same species that originated from different locations. These data indicate segregation of the resistance trait and show that seedling progenies are unsuitable as rootstocks in commercial pear growing. Instead, careful selection of suitable genotypes for propagation is required. Great differences between and within the progenies examined were also observed in vigour and yield efficiency.     

Differences in Virulence and Genomic Features of Strains of 'Candidatus Phytoplasma mali', the Apple Proliferation Agent

ABSTRACT Root and shoot samples from 24 symptomatic or nonsymptomatic apple trees infected with 'Candidatus Phytoplasma mali' were collected at different locations in Germany and France and used to inoculate rootstock M11 top grafted with cv. Golden Delicious. Inoculated trees were monitored over a 12-year period for apple proliferation (AP) symptoms and categorized as not or slightly, moderately, or severely affected. Based on symptomatology, the phytoplasma strains were defined as being avirulent to mildly, moderately, or highly virulent. Determination of phytoplasma titers by quantitative polymerase chain reaction (PCR) with DNA from roots revealed similar phytoplasma concentrations in all virulence groups. Molecular characterization of the strains by differential PCR amplification with five sets of primers resulted in 13 profiles. Six strains that were maintained in periwinkle and tobacco were molecularly characterized in more detail. The genome sizes of these strains as determined by pulsed-field gel electrophoresis using yeast chromosomes as size references ranged between 640 and 680 kb. Cleavage of the chromosome with the rare cutting restriction enzymes ApaI, BamHI, BssHII, MluI, and SmaI resulted in macro fragment patterns distinctly different in all strains. Similar results were obtained by Southern blot hybridization with three probes derived from strain AT. Differential PCR amplification at an annealing temperature of 52 degrees C using eight primer pairs derived from strain AT revealed heterogeneity of target sequences among all strains. Based on these results, there is considerable variability in virulence and genomic traits in 'Ca. P. mali'. However, correlations between molecular markers and virulence or phytoplasma titer could not be identified.     

Genetic variability and the inheritance of resistance to cedar-apple rust in apple

Thirteen apple cultivars and selections were evaluated in a greenhouse for their reaction to cedar-apple rust inoculation Five of the cultivars selections developed aecial lesions on their leaves whereas the sixth cultivar Jonathan, showed only pycnial lesions. The responses of the remaining seven resistant cultivars selections ranged from a lack of any visible symptoms to the presence of discrete flecks or continuous chlorotic mottles Quantitative parameters were used for statistical analysis; these included the highest number of pycnial lesions on a leaf/plant ( N ). the largest diameter of pycnial lesions on any leaf/plant (D)), and the calculated infection rating ( IR = ND ). Significant differences were observed among cultivars selections for variables N. D. and IR . Segregation ratios among progenies derived from 16 controlled crosses indicated that resistance to cedar-apple rust was conditioned by two major genes, and both were required in dominant form to confer resistance. However, in three crosses the dual-gene hypothesis was inadequate to explain the reaction of seedlings.     

The effect of three irrigation practices on phytophthora crown and root rot of apple trees under field conditions

The effect of microjet, drip, and two durations of sprinkler irrigation systems on phytophthora crown and root rot of apple trees was examined under field conditions. This eight year study indicates that crown and root rot caused byPhytophthora cactorum was most severe where young MM. 106 rootstock trees were watered by microjet irrigation for 2.3 h each day. There was no difference in infection byP. cactorum when trees were irrigated either by drip or sprinkler irrigation systems. The MM.106 apple rootstock trees watered by drip irrigation for 2.6 h each day were least affected by phytophthora crown and root rot.     

The insect vector Cacopsylla picta vertically transmits the bacterium ‘Candidatus Phytoplasma mali’ to its progeny

The phloem‐sucking psyllid Cacopsylla picta plays an important role in transmitting the bacterium ‘Candidatus Phytoplasma mali’, the agent associated with apple proliferation disease. The psyllid can ingest ‘Ca. Phytoplasma mali’ from infected apple trees and spread the bacterium by subsequently feeding on uninfected trees. Until now, this has been the most important method of ‘Ca. Phytoplasma mali’ transmission. The aim of this study was to investigate whether infected C. picta are able to transmit ‘Ca. Phytoplasma mali’ directly to their progeny. This method of transmission would allow the bacteria to bypass a time‐consuming reproductive cycle in the host plant. Furthermore, this would cause a high number of infected F₁ individuals in the vector population. To address this question, eggs, nymphs and adults derived from infected overwintering adults of C. picta were reared on non‐infected apple saplings and subsequently tested for the presence of ‘Ca. Phytoplasma mali’. In this study it was shown for the first time that infected C. picta individuals transmit ‘Ca. Phytoplasma mali’ to their eggs, nymphs and F₁ adults, thus providing the basis for a more detailed understanding of ‘Ca. Phytoplasma mali’ transmission by C. picta.     

Identification of fruit tree phytoplasmas and their vectors in Bosnia and Herzegovina

Surveys were carried out in autumn 2004 and spring 2005 in the traditional areas dedicated to pome and stone fruit cultivation in Bosnia and Herzegovina to assess the presence, distribution and incidence of phytoplasma diseases in fruit trees. The occurrence of psyllid vectors was also considered. The detection of phytoplasmas in plant and insect samples and their identification were carried out by symptom observations in the field, double antibody sandwich-enzyme linked immunosorbent assay (DAS-ELISA), nested polymerase chain reaction (nested-PCR) and restriction fragment length polymorphism (RFLP) analyses. Laboratory analyses showed the presence of phytoplasmas belonging to: (i) 16SrX group, subgroup A (' Candidatus Phytoplasma mali') in 23 out of 25 apple samples, in 4 groups out of 18 of Cacopsylla picta (synonym Cacopsylla costalis ) and in 2 groups out of 9 of Cacopsylla melanoneura ; (ii) 16SrX group, subgroup C (' Candidatus Phytoplasma pyri') in 11 out of 30 pears samples and in 2 groups out of 9 of Cacopsylla pyri ; (iii) 16SrX group, subgroup B (' Candidatus Phytoplasma prunorum') in 4 apricots, 2 peaches out of 42 stone fruit samples and in 1 group out of 14 of Cacopsylla pruni . The presence of different subtypes of Candidatus Phytoplasma mali, both in apple trees and in insects, was proven.     

Resistance response of the tomato rootstock SC 6301 to <Emphasis Type="Italic">Meloidogyne javanica</Emphasis> in a plastic house

Nematode reproduction on the nematode-susceptible tomato cv. Durinta grafted onto the Mi-resistance gene tomato rootstock SC 6301 was compared to the Mi-resistance gene tomato cv. Monika in a plastic house infested with Meloidogyne javanica. The ungrafted susceptible cv. Durinta was included as a control for reference. Final soil population densities were lower (P ≤ 0.05) on the resistant than susceptible cultivar but intermediate values were recorded on the rootstock SC 6301. The lowest numbers of eggs per gram root were recorded on the resistant cultivar followed by those on the rootstock; in both cases, they were lower (P < 0.05) than on the susceptible control. Cumulative yield (kilogram per square meter) was higher (P < 0.05) on the resistant than susceptible cultivar whether or not it had been grafted. The rootstock SC 6301 provided an intermediate resistance response to M. javanica and was less effective than the resistant cultivar in suppressing nematode populations and plant damage under the experimental conditions of this study.     

Traditional and commercial apple and pear cultivars as sources of resistance to fireblight1

In Hungary, fireblight research programmes were initiated on pear in 1999 and on apple in 2000, with the aim of evaluating the susceptibility or resistance of commercial cultivars. Sources of resistance for future breeding were also sought among traditional apple cultivars collected from Ukraine and pear cultivars in the Hungarian gene bank (Szigetcsép). Experiments were done under secure conditions. Inocula were mixtures of characteristic Erwinia amylovora isolates from pear and apple in Hungary. Host responses (symptom development, disease severity and multiplication rate of bacterial cells in host tissues) were assessed on shoots, flowers and fruits. About 30 pear and 30 apple cultivars, and 35 apple hybrids, were tested and grouped into four categories for pear and three for apple. Of the pear cultivars tested, 50% were susceptible, 30% moderately susceptible and only 10% of low susceptibility. Different plant organs occasionally displayed different responses. Members of the last two groups might serve as useful candidates for growing under IPM conditions. Among the traditional Hungarian varieties tested, we found high resistance in ‘Sikulai’ and ‘Szemes alma’, which could be used as sources of fireblight resistance in breeding programmes and also grown in organic orchards. Furthermore, among the offspring of the apple ‘Prima’ (scab‐resistant), we have found highly resistant lines.     

Screening for resistance to Didymella bryoniae in rootstocks of melon

Glasshouse evaluations of rootstocks of melon for resistance to Didymella bryoniae were conducted on different cucurbits previously selected as resistant or partially resistant to race 1,2 of Fusarium oxysporum f. sp. melonis. Cucumis anguria, C. ficifolius, C. figarei, C. metuliferus, C. zeyheri and Benincasa hispida showed a very high degree of resistance to D. bryoniae both on leaves and stems. Among the commercial rootstocks, Cucurbita hybrids ELSI, ES 99-13, RS 841, displayed a similar level of resistance. Stem inoculation of three cucurbit species grafted with susceptible melon cv. Proteo determined the occurrence of limited symptoms, but the lesions remained confined in the rootstock not affecting the grafted plant. Cultivation of susceptible melon cultivars grafted on resistant rootstocks may represent an efficient method for controlling Didymella crown rot and Fusarium wilt.     

Breeding for resistance: breeding for Plum pox virus resistant apricots (Prunus armeniaca L.) in Spain

Plum pox virus , Dideron type (PPV-D), was first detected in Spain in 1984. Since then, it has spread among Japanese plum trees and apricot trees has been extremely rapid in the main producing areas. In Spain, breeding for resistance was the only efficient method for controlling the disease on apricot. Two breeding programmes are currently producing new hybrids resistant to the disease. The main problem encountered by both programmes is the difficult procedure needed for screening the trait that delays the programmes. Nevertheless, more than 8000 seedlings have been produced, two new varieties have been released and several advanced selections are under study. The procedure for screening sharka resistance has varied by techniques and cultivars used which has resulted in different hypotheses about inheritance of the trait. Additionally, several studies on mapping and molecular markers in progress could provide markers for molecular assisted selection that can increase the breeding efficiency.     

Phytoplasma transmission by in vitro graft inoculation as a basis for a preliminary screening method for resistance in fruit trees

In vitro grafting was tested as a technique for inoculating Prunus rootstock Prunus marianna GF 8-1 with European stone fruit yellows (ESFY) phytoplasmas and apple rootstock Malus pumila MM106 with apple proliferation (AP) phytoplasmas. In vitro shoot cultures of ESFY-infected Prunus marianna GF 8-1 and AP-infected Malus pumila MM106 were used as graft inoculum to transmit the phytoplasmas to the respective healthy rootstock. Phytoplasma transmission was assessed after a graft contact of 1, 2 or 3 months. Healthy autografts were used as controls to monitor parameters of in vitro grafting. Successful graft union formation ranged from 58 to 79% irrespective of the plant species and the sanitary state of the graft. Pathogen-specific polymerase chain reaction (PCR) was used to test the inoculated rootstocks for the presence of ESFY and AP phytoplasmas, respectively. The rate of ESFY phytoplasma transmission in successful Prunus -grafts increased from 69 to 94% with the time of contact. AP phytoplasma transmission to Malus occurred in 80 to 97% of successful grafts. To our knowledge this is the first report of phytoplasma transmission by grafting in vitro . The results provide a good basis for the establishment of a preliminary in vitro screening method for phytoplasma resistance in Prunus and Malus .     

On the apple proliferation symptom display and the canopy colonization pattern of “<Emphasis Type="Italic">Candidatus</Emphasis> Phytoplasma mali” in apple trees

Notwithstanding the availability of several different real time PCR protocols for “Candidatus Phytoplasma mali”, it is still unclear how informative is the estimation of the concentration of phytoplasma cells in the leaves of apple proliferation infected trees, and how the reliability of the estimations may be affected by an erratic and uneven distribution of the pathogen in the host. Here we investigated these issues systematically and showed that phytoplasma concentration varies significantly among seasons, but not between two cultivars that appeared to have different degree of susceptibility on the basis of the symptoms displayed. In fully symptomatic trees sampled at the end of the season the phytoplasmas were detectable in most leaves, but in more than half of the leaves at low concentrations. Both the pattern of colonization of the canopy and the amount of phytoplasmas varied greatly in trees that show symptom remission, although a direct relation between symptom severity and colonization could not be established. The sampling of the apple canopy for the purpose of evaluation of concentration of “Candidatus Phytoplasma mali” should take into consideration the complex pattern of colonization and seasonal variation.     

小菜蛾不同抗性品系及其杂交F_1代的生物适合度

构建了小菜蛾抗阿维菌素(A)、抗高效氯氰菊酯(B)和抗杀虫双(D)3个抗性品系及其6个杂交F1代(抗性品系分别两两杂交)以及1个敏感品系(S)的种群生命表,并计算了相对生物适合度。结果表明:A、B和D 3个抗性品系的相对生物适合度均比敏感品系S(生物适合度为1.0)低,分别为0.60、0.77和0.53;6个杂交F1代A♀+B♂、A♂+B♀、A♀+D♂、A♂+D♀、B♂+D♀和B♀+D♂的生物适合度分别为0.67、0.53、0.67、0.74、0.73和0.80,也比敏感品系的低,但和抗性品系的适合度相近或高于抗性品系。     

Highly infested soils undermine the use of resistant olive rootstocks as a control method of verticillium wilt

Verticillium wilt of olive (VWO) is probably the most devastating fungal disease for olive trees worldwide, and currently the main cultivars are susceptible or moderately susceptible to this disease. The evaluation of resistant cultivars as rootstocks to control the disease has scarcely been explored, and mainly in short-term studies under controlled conditions, which usually do not correspond with field evaluations. The main objective of this study was to assess the responses to VWO of different scion × rootstock combinations of the olive cultivars Picual, Arbequina, Changlot Real, and Frantoio in a long-term field experiment with a soil highly infested with the defoliating pathotype of Verticillium dahliae. The results showed that grafting the susceptible cultivar Picual onto resistant rootstocks delayed the onset of the disease symptoms; however, after 4 years, it was observed that all combinations that contain Picual (a) were extensively colonized by V. dahliae; (b) developed severe symptoms of the disease; and (c) had plant mortality similar to Picual growing on its own roots. This result highlights the importance of long-term field experiments to evaluate VWO and shows that grafting susceptible olive cultivars onto resistant ones does not provide a durable control of VWO under high inoculum potential, as V. dahliae is able to progress through the resistant rootstock and then extensively colonize and kill the susceptible scion. However, the high inoculum potential observed in this study does not allow us to consider the evaluated resistant cultivars as completely ineffective under lower inoculum densities.     

THE INFLUENCE OF SIMAZINE ON SHOOT AND ROOT GROWTH OF APPLES AND PLUMS

Summary. In loamy soil with a low humus content (0·8% organic carbon) simazine at a concentration of 2'5 ppm reduced growth of shoots, roots and trunk diameter in 1-year-old scions of five apple varieties on M IX rootstock. The most susceptible was Cox's Orange Pippin; 5 ppm was lethal for this variety only. In experiments with vertically divided pots, where one part of the root system developed in soil with simazine (2–5 ppm and 5–0 ppm for apple and 5·0 ppm for plum) and the other part in simazine-free soil, there was less effect on shoot growth and less leaf damage than where all the soil contained simazine. Growth of that part of the root system in soil containing simazine was stimulated.